Rotary electrical machine with an optimised configuration

ABSTRACT

The invention relates mainly to a rotating electrical machine of a motor vehicle, comprising a rotor (12) haying an axis (X) comprising at least one permanent magnet (20) and a stator (11) surrounding the rotor and comprising a body (24) provided with a plurality of slots (30) and an electrical winding (25), the winding comprising phase windings (26) arranged in the slots, each phase winding being formed by at least one conductor (35). The rotor (12) comprises 3, 4 or 5 pairs of poles. The stator comprises two three-phase systems, each formed by three delta connected phase windings (26). The number of conductors (35) per slot (30) is strictly greater than 2 and each conductor has an active portion (40) inserted in a corresponding slot (30), the active portion with a substantially rectangular section being of is radial length (L2) smaller than or equal to 3.6 mm.

The present invention relates to a rotary electrical machine with anoptimised configuration.

The invention has a particularly advantageous, but non-exclusiveapplication with high-power reversible electrical machines which canoperate in alternator mode and in motor mode, coupled with a hostelement, such as a gearbox.

In a known manner, rotary electrical machines comprise a stator and arotor integral with a shaft. The rotor can be integral with a drivingand/or driven shaft, and can belong to a rotary electrical machine inthe form of an alternator, an electric motor, or a reversible machinewhich can operate in both modes. In alternator mode, when the rotor isrotating, it induces a magnetic field on the stator, which transformsthis field into electric current, in order to supply the electricalconsumers of the vehicle with power and recharge the battery. In motormode, the stator is supplied electrically and induces a magnetic fieldwhich rotates the rotor in order to start the thermal engine and/orparticipate in the traction of the vehicle, autonomously or incombination with the thermal engine.

The stator is fitted in a housing which is configured to rotate theshaft on bearings by means of roller bearings. In addition, the statorcomprises a body constituted by a stack of thin metal plates forming acrown, the inner face of which is provided with notches open towards theinterior in order to receive an electrical winding formed by phasewindings. These windings pass through the notches in the body of thestator, and form chignons which project on both sides of the body of thestator. The phase windings are obtained for example from a continuouswire covered with enamel, or from conductive elements in the form ofpins connected to one another by welding. These windings are polyphasewindings connected in the form of a star or a triangle, the outputs ofwhich are connected to an inverter which also operates as a rectifierbridge.

With this type of machine, the speed of rotation of the machine affectsthe voltage supplied, and therefore the power of the machine. Thus, thehigher the speed of rotation, the greater the power is. For synchronousmachines, beyond a certain speed of rotation, in order to maximise thepower of the machine, it is important to be able to deflux the saidmachine. FIG. 1 represents characteristic torque and power curvesaccording to the speed of rotation of an electrical machine of thistype, rotating respectively in the motor mode M_mth (cf. characteristictorque curve C1 and characteristic power curve C2) and in the generatormode M_gen (cf. characteristic torque curve C3 and characteristic powercurve C4). A defluxing range P_def is defined by reference to a ratiobetween a maximal speed of rotation at constant torque N1 divided by themaximal speed of rotation N2 of the electrical machine. Since thisdefluxing ratio is high (greater than 2.5), the machine can operate athigh speed whilst being in a state of quasi short-circuit.

In order to optimise the operation of the machine, in particular inorder to be able to reach high speeds of operation and therefore highpower, it is necessary for the machine to have good resistance to theshort-circuit current in a steady-state. This optimisation of themachine must also take into account other parameters such as thecompactness of the machine, which is an important parameter for theintegration of the said machine in the vehicle, as well as the thermalperformance of the machine, which is also an important parameter, bothfor the safety of the users, and in order not to damage the machine. Theobjective of the invention is thus to guarantee the resistance to theshort-circuit current in the steady-state, whilst optimising thecompactness and thermal characteristics of the electrical machine.

For this purpose, the subject of the present invention is a rotaryelectrical machine of a motor vehicle. According to the invention, themachine comprises a rotor which extends along an axis of rotation, andcomprises at least one permanent magnet, and a stator which surroundsthe rotor and comprises a body provided with a plurality of notches andan electrical winding, with the winding comprising phase windingsdisposed in the notches, each phase winding being formed by at least oneconductor. In addition, according to the invention, the rotor comprises3 or 4 or 5 pairs of poles, and the stator comprises two three-phasesystems each formed by three phase windings with delta coupling. Inaddition, according to the invention, the number of conductors per notchis strictly greater than 2, and each conductor has an active portioninserted in a corresponding notch, the active portion with asubstantially rectangular cross-section having a radial length of 3.6 mmor less.

The fact of having two three-phase systems makes it possible to simplifythe arrangement of the power modules, and therefore makes it possible toobtain a machine which can be more compact. In addition, the coupling ofthe windings in the form of a triangle makes it possible not to have aneutral point, and therefore improves the compactness of the machine.The fact of having a substantially rectangular cross-section of wiremakes it possible to improve the coefficient of filling of theconductors in the notches, and therefore to improve the power of themachine. Substantially rectangular cross-section means the fact that thecorners of the conductors can be slightly rounded for productionreasons. A number of conductors per notch which is strictly greater thantwo makes it possible to obtain a greater degree of latitude in terms ofthe choice of the number of turns per winding. In addition, the factthat the radial width of the conductors is 3.6 mm or less, associatedwith a number of pairs of poles of the rotor of between 3 and 5, makesit possible to minimise the resistance of the conductors, in order thusto limit the Joule losses of the conductors. All of these parameterstaken together therefore give rise to improved thermal resistance,improved resistance to the short-circuit current in a steady-state, andimproved compactness of the rotary electrical machine. The rotaryelectrical machine can thus operate safely at a higher speed.

According to one embodiment, the two three-phase systems are independentfrom one another, and the rotary electrical machine comprises aninverter comprising two independent modules which are each connected toa three-phase system.

According to one embodiment, the inverter is connected to a directcurrent bus with a voltage of between 30 and 60 V.

According to one embodiment, an orthoradial length of an active portionof the conductor is 1.4 mm or more.

According to one embodiment, an outer diameter of the stator body isbetween 80 mm and 180 mm For example, the outer diameter of the statorbody is selected from amongst one of the following values: 80, 90, 100,110, 153, 161 and 180 mm.

According to one embodiment, a maximal power of the said rotaryelectrical machine is between 8 kW and 30 kW.

According to one embodiment, the number of conductors per notch is even.

According to one embodiment, the number of conductors per notch is equalto 4. As a variant, the number of conductors per notch can be equal to6, 8 or also 10.

According to one embodiment, the conductors are aligned radiallyrelative to one another in the interior of a corresponding notch.

According to one embodiment, each phase winding is formed from aplurality of conductors which in particular are in the form of pinsconnected electrically to one another. For example the pins extend inthe form of a “U” comprising two active parts extending in respectivenotches, and a connection portion which connects the two active parts.Preferably, a phase winding is formed by welding to one another the freeends of the active parts of different pins. Free ends means the ends ofthe active parts which are not connected to the connection portion.

According to one embodiment, each phase winding is formed from acontinuous conductor. This continuous conductor is for example a wire.

According to one embodiment, the conductor wire comprises activeportions with a substantially rectangular cross-section, and portions ofconnection between two adjacent active portions with a cross-sectionwhich is rounded, and in particular substantially round.

According to one embodiment, the conductors have a rectangularcross-section with rounded corners.

According to one embodiment, the said rotary electrical machinecomprises a cooling liquid circuit.

According to one embodiment, the machine is a synchronous machine.

According to one embodiment, the machine is a machine with permanentmagnets.

According to one embodiment, the said rotary electrical machine is inthe form of a rotor, a generator, or a reversible electrical machine.

The invention will be better understood by reading the followingdescription and examining the figures which accompany it. These figuresare provided purely by way of illustration, and in no way limit theinvention.

FIG. 1, already described, shows the characteristic torque and powercurves according to the speed of rotation of a rotary electrical machineused within the context of the invention.

FIG. 2 is a view in longitudinal cross-section of a rotary electricalmachine according to an embodiment of the present invention.

FIG. 3 is a view in perspective of the wound stator and of the rotor ofthe rotary electrical machine in FIG. 2.

FIG. 4 is a view in partial transverse cross-section of the rotor and ofthe wound stator according to an embodiment of the present invention.

FIG. 5 shows graphic representations of the development of the ratiobetween the resistance of an electrical high-frequency stator conductorand the resistance of an electrical low-frequency stator conductoraccording to the radial dimension of an active portion of a statorconductor, respectively for a rotor with 3 and 5 pairs of poles.

FIG. 6 represents the development of the total axial height of therotary electrical machine according to the number of pairs of poles ofthe rotor.

Elements which are identical, similar or analogous retain the samereference from one figure to another.

Hereinafter in the description, a “front” element means an element whichis situated on the side of the drive part, such as on the side of thepinion supported by the shaft of the machine, and “rear” element meansan element which is situated on the opposite side relative to the axisof rotation X of the machine.

FIG. 2 shows a rotary electrical machine 10 comprising a polyphasestator 11 surrounding a rotor 12 fitted on a shaft 13 extending along anaxis X corresponding to the axis of the machine. The stator 11 surroundsthe rotor 12 with the presence of an air gap between the inner peripheryof the stator 11 and the outer periphery of the rotor 12. The stator 11is fitted in a housing 14 provided with a front bearing 15 and a rearbearing 16 which supports the shaft 13 with rotation.

This electrical machine 10 can be designed to be coupled to a gearboxbelonging to a motor vehicle traction chain. In another configuration,the electrical machine 10 can be coupled to a crankshaft of the vehicle,or also directly to the traction chain of the wheels of the vehicle. Forexample, the machine 10 can be coupled to a part of the vehicle by apinion 17 as represented in FIG. 2. As a variant, the machine 10 can becoupled to a part of the vehicle by a pulley or any other couplingmeans.

The machine 10 can operate in an alternator mode, in order in particularto supply energy to the battery and to the on-board network of thevehicle, and in a motor mode, not only in order to ensure the startingof the thermal engine of the vehicle, but also to participate in thetraction of the vehicle, alone or in combination with the thermalengine. As a variant, the electrical machine 10 can be implanted on anaxle of the motor vehicle, in particular a rear axle. As a variant, theelectrical machine 10 is in the form of an electric motor or anon-reversible generator. The power of the electrical machine 10 isadvantageously between 8 kW and 30 kW.

In the example in FIG. 2, the rotor 12 comprises a body 19 in the formof a set of metal plates. Permanent magnets 20 can be implanted in theinterior of cavities 21 according to a configuration in the form of a“V”, as illustrated in FIG. 4, or they can be implanted radially in theinterior of the set of metal plates, and the lateral faces opposite oneanother of two consecutive magnets 20 can have the same polarity, asillustrated in FIG. 3. The rotor 12 is then of the flux concentrationtype. Alternatively, the permanent magnets 20 extend orthoradially inthe interior of the cavities 21 in the body 19. The magnets 20 can bemade of rare earth or ferrite, according to the applications and thepower required from the machine 10.

In addition, as can be seen in FIGS. 3 and 4, the stator 11 comprises abody 24 constituted by a set of metal plates, as well as an electricalwinding 25. The body 24 is formed by a stack of metal plate sheets whichare independent from one another, and are retained in the form of a setby means of an appropriate securing system. As can be seen in FIG. 4,the body 24 is provided with teeth 28, which delimit in pairs notches 30for the fitting of the stator winding 25. Thus, two successive notches30 are separated from one another by a tooth 28. Preferably, an outerdiameter L1 of the stator body 24 is between 80 and 180 mm.Advantageously, the outer diameter L1 of the stator body 24 is selectedfrom amongst one of the following values: 80, 90, 100, 110, 153, 161 and180 mm.

The winding 25 comprises an assembly of phase windings 26 which passthrough the notches 30 and form chignons 33 extending projecting on bothsides of the stator body 24, as shown in FIGS. 2 and 3. The outputs ofthe phase windings 26 are connected to an inverter 34, which can alsooperate as a rectifier bridge. For this purpose, the inverter 34comprises power modules provided with power switching elements, such astransistors of the MOS type, connected to the phase outputs.

Each phase winding 26 can be formed from a plurality of conductors 35constituted by pins 37. These pins 37 can have the form of a “U”, theends of the branches of which are connected to one another for exampleby welding. As a variant, each phase winding 26 is formed from acontinuous conductive wire wound in the interior of the stator 11 in thenotches 30, in order to form one or a plurality of turns. In all cases,a distinction is made between the active portions 40 of a conductor 35situated in the interior of the notches 30, and connection portions 41which connect two adjacent active portions 40 to one another. The activeportions 40 thus correspond to the portions of the conductors 35 whichextend axially in the interior of the notches 30, whereas the connectionportions 41 extend circumferentially in the interior of the chignons 33,in order to connect the active portions 40 to one another. Theconductors 35 can for example be made of a material based on enamelledcopper.

The phase windings 26 are each associated with a series of notches 30,such that each notch 30 receives several times the conductors 35 of thesame phase. Advantageously, the stator 11 comprises two three-phasesystems which are preferably independent, i.e. A1, B1, C1 and A2, B2, C2each formed by three phase windings 26, as illustrated in FIG. 4. Thismakes it possible to guarantee the compactness of the inverter 34 byfacilitating the arrangement of the power modules of the inverter 34 ina cylinder which is situated at the rear of the machine for theintegrated systems (cf. FIG. 2) or in a substantially parallelepipedvolume on the side of the machine 10.

Each three-phase system A1, B1, C1; A2, B2, C2 is coupled in the form ofa triangle in order to optimise the compactness of the electricalmachine 10. In fact, in comparison with a coupling of the double startype, the double triangle coupling makes it possible to avoid theintegration of the neutral bars in the wound stator 11, which arerelatively cumbersome.

Each three-phase system A1, B1, C1; A2, B2, C2 is connected electricallyto an independent module of the inverter 34. Each independent modulecomprises power elements and a control module which is dedicated to thecorresponding three-phase system. The two independent modules areaccommodated in a single casing of the inverter 34 which tops the rearbearing. The inverter 34 is preferably connected to a direct current buswith a voltage of between 30 and 60 V.

In this example, two consecutive notches 30 of a series associated witha phase are separated by adjacent notches 30 each corresponding toanother series of notches associated with one of the other phases. Thus,when there are K phases, the conductors 35 of a single phase winding 26are all inserted every K+1 notches. For example, if the winding of thephase A1 is inserted in notch no. 1, it is then inserted in the 7^(th)notch for a machine with two three-phase systems, i.e. K=6. It should benoted that, in the configuration represented in FIG. 4, the phases ofthe two systems alternate according to the circumference of the stator11. In this example, taking into consideration the circumferentialdirection, the first notch comprises the phase A1, the second notchcomprises the phase A2, the third notch comprises the phase B1, thefourth notch comprises the phase B2, the fifth notch comprises the phaseC1, and the sixth notch comprises the phase C2. According to a variantembodiment, another phase configuration can be envisaged.

The conductors 35 advantageously have a substantially rectangularcross-section, at least in their active portion 40, and they are alignedradially relative to one another in the interior of the correspondingnotch 30. A winding configuration of this type arranged with conductors35 with a substantially rectangular cross-section makes it possible toreduce the height of the chignons 33, and assists the compactness of themachine in comparison with a random winding made of round wire.According to a particular embodiment of winding with continuous wire,the conductive wires can be pressed only in the active portions 40, andhave a round cross-section in the connection portions 41. Thesubstantially rectangular cross-section of the active portions 40 canhave rounded corners in order not to damage the enamel As a variant, theconductors 35 can have a substantially square cross-section.

The number of conductors 35 in the interior of each notch 30 isadvantageously strictly more than two in order to have a degree offreedom in terms of the choice of the number of turns per phase winding26. Preferably, the number of conductors 35 per notch is even. In thiscase it is equal to 4, but as a variant it could be different, and inparticular equal to 6, 8 or 10.

At a high electrical frequency and therefore at a high speed ofrotation, the conductors 35 are subjected to pellicular and proximityeffects which result in making the density of current non-uniform in theconductor 35. This leads to an increase in the apparent resistance ofthe conductor 35. This increase in resistance is conventionallyquantified by a ratio between the AC resistance at high-frequency andthe DC resistance of the same conductor 35 at a very low frequency of afew Hertz.

The electrical resistance therefore depends on the temperature, thedimensions of the stator 11, the dimensions of the conductors, and theelectrical frequency fe, which is associated with the speed of rotationN in revolutions per minute of the machine by means of the followingformula: fe=(N×p)/60, p being the number of pairs of poles of the rotor12.

The increase in this resistance gives rise to additional Joule losses,and involves an increase in the size of the electrical machine 10 inorder to be able to discharge the calories, for example by increasingthe size of a cooling liquid chamber 44 described in greater detailhereinafter.

The main factor which affects the AC resistance is the radial length L2of the conductor 35 in the interior of the notch 30, as well as theelectrical frequency fe which is associated with the polarity of therotor 12 for the same speed of rotation.

For an electrical machine 10 with a stator diameter L1 of approximately160 mm and a speed of rotation of 20,000 rpm, FIG. 5 represents thedevelopment of the ratio between the AC resistance of a stator conductorat a high frequency and the DC resistance of this stator conductor 35 ata low frequency according to the radial length L2 of the active portion40 of a conductor 35, respectively for a rotor with 3 pairs of poles(cf. curve C5) and with 5 pairs of poles (cf. curve C6).

It is found that, for a given limit Lim of losses which can bedischarged by the electrical machine 10, the maximal radial length L2 ofthe conductor 35 is 3.6 mm for a machine with five pairs of poles. Avalue of this type guarantees adequate performance for a machine withthree pairs of poles, the AC/DC ratio of which is globally lower thanthat of the machine with five pairs of poles.

In addition, the orthoradial length L3 of an active portion 40 is 1.4 mmor more. This length L3 has little effect on the AC resistance of theconductors 35. In fact, as can be seen in FIG. 5 by means of thedifferent points C7, for a given radial length L2, and by varying theorthoradial length L3 of the conductors 35, the value of the AC/DC ratiovaries only very slightly.

FIG. 6 represents the development of the total axial height L4 of thestator 11 of the electrical machine (cf. FIG. 2) according to the numberof pairs of poles p of the rotor 12. Axial height means the distancebetween the two ends of the front and rear chignons 33. This figureshows that a rotor 12 with fewer than three pairs of poles leads to anincrease in the total height L4 of the machine, since the height of thechignons 33 is substantially proportional to the polarity. In fact, thefewer poles there are in the machine, the more the distance between thepoles increases. Thus, the notches through which a single phase windingpasses are further apart from one another, and the portions of theconductors which form the chignons must therefore be larger. On theother hand, a polarity of more than five pairs of poles gives rise totoo many losses. In these conditions, the optimal polarity is between 3and 5 pairs of poles, i.e. the rotor 12 can comprise 3 or 4 or 5 pairsof poles.

The rotary electrical machine 10 can comprise a cooling liquid circuitcomprising a cooling liquid input and output in order to make the liquidcirculate in a chamber 44 provided on the outer periphery of the stator11 as shown in FIG. 2. The electrical machine 10 can thus be cooled bywater or by oil. According to a variant embodiment, the machine can becooled by air, for example by means of a fan.

It will be appreciated that the foregoing description has been providedpurely by way of example and does not limit the scope of the invention,a departure from which would not be constituted by replacing thedifferent elements by any other equivalents.

In addition, the different characteristics, variants, and/or embodimentsof the present invention can be associated with one another according todifferent combinations, provided that they are not incompatible ormutually exclusive.

1. A rotary electrical machine of a motor vehicle, comprising: a rotorwhich extends along an axis of rotation comprising at least onepermanent magnet; and a stator which surrounds the rotor and comprises abody provided with a plurality of notches and an electrical winding,with the winding comprising phase windings disposed in the notches, eachphase winding being formed by at least one conductor, wherein, in therotary electrical machine: the rotor comprises 3 or 4 or 5 pairs ofpoles, the stator comprises two three-phase systems each formed by threephase windings with delta coupling, and the number of conductors pernotch is greater than 2, and each conductor has an active portioninserted in a corresponding notch, the active portion with asubstantially rectangular cross-section having a radial length of 3.6 mmor less.
 2. The rotary electrical machine according to claim 1, whereinthe two three-phase systems are independent from one another, themachine further comprising an inverter comprising two independentmodules which are each connected to a three-phase system.
 3. The rotaryelectrical machine according to claim 2, wherein the inverter isconnected to a direct current bus with a voltage of between 30 and 60 V.4. The rotary electrical machine according to claim 1, wherein anorthoradial length of an active portion of a conductor is 1.4 mm ormore.
 5. The rotary electrical machine according to claim 1, wherein anouter diameter of the stator body is between 80 mm and 180 mm.
 6. Therotary electrical machine according to claim 5, wherein the outerdiameter of the stator body is selected from amongst one of thefollowing values: 80, 90, 100, 110, 153, 161 and 180 mm.
 7. The rotaryelectrical machine according to claim 1, wherein a maximal power of thesaid rotary electrical machine is between 8 kW and 30 kW.
 8. The rotaryelectrical machine according to claim 1, wherein the number ofconductors per notch is even.
 9. The rotary electrical machine accordingto claim 8, wherein the number of conductors per notch is equal to 4.10. The rotary electrical machine according to claim 1, wherein theconductors are aligned radially relative to one another in the interiorof a corresponding notch.
 11. The rotary electrical machine according toclaim 1, wherein each phase winding is formed from a plurality ofconductors which are in the form of pins connected electrically to oneanother.
 12. The rotary electrical machine according to claim 1, whereineach phase winding is formed from a continuous conductor.
 13. The rotaryelectrical machine according to claim 1, wherein the rotary electricalmachine it is in the form of a rotor, a generator, or a reversibleelectrical machine.